Aspects of the invention pertain generally to the field of electronic thermometers and more particularly to the field of fast response electronic thermometers employing a sensor probe.
Electronic thermometers are widely used in the healthcare field for measuring patient's body temperature. Typical electronic thermometers have the form of a probe with an elongated shaft portion. Electronic temperature sensors such as thermistors or other temperature-sensitive elements are contained within the shaft portion. Additional electronics connected to the electronic sensor components may be contained within a base unit connected by wire to the shaft portion or may be contained within a handle of the shaft portion, for example. Electronic components receive input from the sensor components to compute the patient's temperature. The temperature is then typically displayed on a visual output device such as a seven, or fourteen, segment numerical display device. Additional features of known electronic thermometers include audible temperature level notification such as a beep or tone alert signal. A disposable cover or sheath is typically fitted over the shaft portion and disposed after each use of the thermometer for sanitary reasons.
Electronic thermometers have many advantages over conventional thermometers and have widely replaced the use of conventional glass thermometers in the healthcare field. For example, electronic thermometers do not require costly sterilization procedures and do not present the dangers associated with mercury or broken glass causing injury to a patient. Furthermore, electronic thermometers generally have a faster response time than glass thermometers and provide very precise and accurate temperature measurement information.
Despite the response time improvements over glass thermometers, some known electronic thermometers have unacceptably long response time. The long response time is primarily due to the thermal mass of the probe together with the sensor components. The thermal mass of the probe and the sensor components may take several minutes to reach the actual body temperature of the patient being measured. The thermal mass of the probe typically begins a measurement cycle at a lower temperature than the patient being measured and absorbs heat from the patient until the patient and the thermal mass of the probe reach thermal equilibrium. Therefore, the thermal mass of the probe prevents the sensor temperature from instantaneously reaching a patients body temperature.
Electronic thermometers in the art are known having improved response times that are achieved using a number of different techniques. One technique known in the art employs thermally conductive material such as metal in the probe tip between the patient contact area and the temperature sensor. Another technique uses a very thin layer of material between the patient contact area and the temperature sensors. Both of these techniques improve response time somewhat but still allow time to be wasted while heat from the patient flows to the thermal mass of the probe instead of the temperature sensors.
Previously known electronic thermometers have employed electric heater elements in the probe shaft to bring the temperature of the thermal mass of the probe shaft and probe tip closer to the temperature of the patient prior to taking temperature measurements. Temperature sensor readings are used in known methods to control electric current to the heater element. Time is saved because less heat must be transferred from the patient to the thermal mass of the probe before the temperature sensors reach thermal equilibrium with the patient.
The response time of electronic thermometers has also been improved by methods that do not involve heating the probe shaft or tip. Predictive type thermometers are known for example, wherein a set of early temperature measurements are read by the electronics of the thermometer and a mathematical algorithm is applied to extrapolate to a final estimated equilibrium temperature. Various prediction type thermometers are known which improve response time and provide accurate temperature estimations. Still other methods of improving the response time of electronic thermometers are known which combine heating methods with prediction methods. For example, one predictive-type clinical thermometer automatically switches between a plurality of prediction functions to determine a final predicted temperature. The thermometer monitors the measured results of the thermometer for a set time before applying an initial predictive function to the measured results. The thermometer then monitors the ability of the initial predictive function to predict the measured results. Where the measured temperature results do not follow the initially applied prediction function, the thermometer automatically selects another prediction function. Again, the thermometer monitors the ability of this other prediction function to predict the measured results. This process of monitoring and switching to another of a plurality of predictive functions continues until the thermometer determines that a satisfactory prediction is achieved or that a time limit is reached. In other words, without user input or control, the thermometer can select to apply several different predictive functions throughout a single measurement process. This automatic switching from one predictive function to another can add measurement time and ignores any user preference or input regarding desirable prediction time or required accuracy.
Disadvantages of known thermometers leave room for improvement. For example, some thermometers still suffer from relatively long response times, as judged by the user of the thermometer. For prediction algorithms, the goal of decreased response time opposes the goal of increased precision. As response time is reduced, precision decreases, and vice versa. Thus, known thermometer designers have had to make a design choice for the user, constructing thermometers that compromise between decreased response time and increased precision. The problem with making such a choice for all applications, however, is that different thermometer applications may have different requirements and goals. For example, some applications require a very short response time, but do not require an extremely high level of precision. In contrast, other applications do not require a short response time, but do require an extremely high level of precision. Conventional thermometers ignore these user preferences and may spend more time than a user would prefer obtaining a predicted temperature. Conversely, a conventional thermometer may not spend adequate time determining a predicted temperature of sufficient accuracy. A thermometer that allowed the user to determine and adjust the balance between response time and precision based upon the thermometer application would be useful.